1. Field of the Invention
The invention relates to elevators, such as passenger and freight elevators, that operate between two or more floors or landings.
2. Description of Related Art
There are two types of modern elevators, traction elevators and hydraulic elevators. In traction-type elevators, an elevator car is suspended by a wire rope, usually in a hoistway. The rope extends upwardly to the top of the elevator shaft, is directed around an overhead drive pulley, passes over a guide pulley, and thereafter extends downwardly to a counterweight. A motor is coupled to the drive pulley, either directly (a so-called "gearless elevator") or through intermediate gears (a so-called "geared elevator"), such that actuation of the motor selectively raises and lowers the car between floors.
In hydraulic elevators, the weight of the car is supported by one or more hydraulic jacks. In order to raise the car, a motor pumps hydraulic fluid from a reservoir through a control valve into the jacks. To lower the car, the valve is opened to vent the jack, and the weight of the car causes fluid to flow out of the jack and back into the reservoir, and thereby allows the car to descend.
Traction elevators can be designed to operate over a broad range of speeds, depending upon the intended application, and can serve buildings ranging from two stories to skyscrapers. The principal drawbacks of traction elevators are their relatively high cost and the fact that they generally require an overhead penthouse, in order to house the pulleys and motor/drive system. Hydraulic elevators are less costly, but are not capable of operating as fast as traction elevators, and the number of floors that can be serviced is limited.
My prior U.S. Pat. No. 5,572,530 discloses an elevator system in which the car moves up and down using a traction drive instead of an overhead motor and pulley or a hydraulic cylinder. A pair of rollers, which are mounted on a swivel plate, are disposed on either side of a rail and pressed towards the rail to create friction. A motor, which is on the elevator car, drives at least one of the rollers to move the elevator car up or down. Such elevator has the advantages of a traction elevator, in terms of high speed capability and the potential to service high rise buildings, but does not require an overhead penthouse supporting a motor and drive system as in conventional traction elevators.